WHEN Dr. Varenius wrote his Geography, the Secret of making Salt-Water sweet or fresh, was not difcover'd, as he owns in his 13th Chapter, Prop. XI. The World owes this to our ingenious Countryman Mr. Hauton. Mr. Dugdale gives us the Manner of performing this from the Philofophical Tranfactions. It is done firft by a Precipitation made with the Oil of Tartar: then the Sea Water is diftilled. The Furnace used on this Occafion taketh up but little room, and is fo contrived, that with a very fmall Quantity of Wood or Coal, twenty four French Pots of Water may be distilled in a Day; for the 'cooling of which, the aforefaid Gentleman has this new Invention; that inftead of making the Worm pass through a Veffel full of Water, as is the common Practice, he makes it pass through a Hole, made out of the Ship, and enter it again at another; fo that the Water of the Sea performeth the cooling Part. Thirdly, to the two preceeding Operations he joins Filtration, to make a perfect Correction of the Malignity of the Water. This is done by a peculiar Earth, which is mixed and stirred with the distilled Water, and at length fettles to the Bottom. Mr. Hauton declares he had both Reafon and Experience on his Side. The former, because this peculiar Earth, being mixed with the diftilled Waters, blunts the Points of the Volatile Spirits of the Salt, and ferveth them for Sheaths, taking away their force and maligning Sharpness. The fecond, because it had been given to Men and Beafts, without any ill effect

on them.

IN the fame Chapter, Prop. XIV. our Author undertakes to tell us why the Ocean is not enlarged by the great number of Rivers, which

flow

of Letters. flow into it. Sea-War

1. That the Ws of the Eare affigns two Reasons. from the Sca through fubterraneous Mazes of to the Heads of the 2, lofeth intities of Vapours are Rivers. 2. rais'd from the & an; part of which, being refolved into Rain, falls down into the Ocean, and part of them on the Earth.

DR. Jurin, in his Appendix, enlarges on this curious Queftion in the following manner. Since the Ocean conftantly receives a prodigious Quantity of Water, both from Rivers, that exonerate themfelves into it, and from the Air in Dew, Rain and Snow that fall, it is impoffible but that it fhould be enlarged and increafe to an immense Bulk, unless it be as much leffened fome other way. And fince no fuch great increase of the Sea has been observed, and the Bounds of the Ocean and the Earth are found to be in all Ages the fame, it remains that we enquire by what means the Ocean lofes as much Water as it receives from Rain and Rivers flowing into it. There are two Hypothefes among Philofophers; one is, that the Water of the Sea is carried by fubterraneous Conduits, to the Springs of Rivers, and lofes its Saltnefs, by dreining through the Fiffures. The other, that it is occafion'd by the Vapours exhaled from its Surfaces. The Doctor rejects the former, as almoft univerfally exploded; it being difficult, if not impoffible, to explain how the Water of the Ocean, being more depreffed than the very Mouths of the Rivers, can come up to their Springs, which are for the most part on very high Mountains. He therefore inclines to the latter, which is not charged with this Difficulty, there being, according to this Hypothefis, no Neceffity of explaining this, neither to hinder the Growth of

the

the Ocean, nor to fupes wrote hings with Water; both which may lt-Water easily done by the Vapours, which he owriinly know are drawn up from the Su. Worl he Sea. To Worle illuftrate this Hypothefis, IM produces an Experiment made by Dr. Halley on Water falted to the fame Degree with the common Sea Water, and heated to the fame Degree, which that of Air is obferved to be in our hottest Summers, in order to form a Judgment of the Quantity of Vapours exhaled from the Sea. This may be seen at large in the Philofophical Tranfactions, No. 189. Page 366.

CHAP. 14. Prop. IX. We have Mr. des Cartes's mechanical Account, how the general Motion of the Sea, from Eaft to Welt may be caused by the Moon. But, though our Author was a great Admirer of that Philofopher, he looks on this Account as deficient, and profeffes no better Opinion of his accounting for the Flux and Reflux of the Sea, in the fame Chapter, Prop. X. As this is done according to his general Hypothefis of a Plenum and Vortices, it is not admitted by Dr. Jurin and our Annotator. The former afferts that Sir Ifaac Newton has explain'd the Flux and Reflux of the Sea with great Success, from his univerfal Principle of Gravity or Attraction. This he fhews by two Figures at the end of the Book, and refers us to feveral celebrated Writers for farther Satisfaction.

IN the 16th Chapter, Prop. V. the Author undertakes to explain the Origin of Springs. Having produced five different Opinions on this Subject, he gives a 6th, viz. that the Earth again receives whatever Waters it has diffembogued into the Sea, through the Mouths of

Rivers;

Rivers; that the Sea-Water paffes through the hidden Receffes of the Earth, and, being ftrain'd through the many Mazes of theEarth, and through the Sand and Clay, lofeth its faltness and bitterness. He embraces this, as most reasonable, and defends it against four Objections. On this Occafion the learned Dr. Jurin fays, it is probable that all Springs have not the fame Origin; that fome proceed from Rain penetrating through the Fiffures of the Earth, and flowly gliding through the Orifices of Springs: that others, especially fuch as are Salt and near the Sea, take their rife from its Water percolating through the Sands: but that the greatest part, especially fuch as break from the Sides of high Hills, derive their Water from Vapours. This is the great Dr. Halley's Theory, which is reckon'd much more clear than any other, and better fupported.

THE Doctor's Hypothefis is, that these Vapours, being carried every way by the Wind, neceffarily meet with the high Ridges of Mountains, that are difperfed over various Tracts of the Earth; each of which far furpaffes the ufual Height to which the aqueous Vapours of themselves afcend, and on the Tops of which the Air is fo cold and rarified, as to retain but a fmall part of thofe Vapours, that are brought thither by the Winds. The Vapours, meeting with thefe Ridges of Mountains, are there compelled by the Stream of the Air to mount with it to their Tops; where meeting with more rarified Air, they naturally fall down in Drops, pervading the Crannies and Fiffures of the Air, and gleeting into the Caverns of the Hills, the Water thereof gathers into the Basons of Stone or Clay it finds; which being once fill'd, all the Overplus of the Water

runs

runs over, and where it can find a Paffage, breaks out at the Sides of the Hills, and forms Fountains; many of thefe running down the Vallies or Guts between the Ridges of the Hills, and coming to unite, form Rivulets or Brooks; many of these again being united into one common Chanel, form vaft large Rivers, as the Danube or the Rhine.

Varenius, in the fame Chapter, Prop. VI. fpeaking of the River Niger in Africa, tells us, it hides itself under the Mountains of Nubia, and emerges again on the Weft fide of the faid Mountains. Mr. Dugdale, in a Note on this Place, fays that the River, here mention'd, hides itself no where under Ground that we know of; though perhaps we are not certain whether it does or not, because no European has traced it to its Fountain. Only the Zeebe, a large Branch of it, meeting with the Mountains of Nimeamay, is faid to divide itself into feveral Streams, to immerge under them, and emerge again on the North fide of those Mountains. But he is fo cautious of admitting any thing of this Nature, that he declares he does not give this as a Certainty, but looks on all fuch Accounts as mere poetical Fictions, as in all probability they are.

CHAP. 17. Prop. VI. our Author attempts to account for the Caufe or Generation of acid Waters, their Difference, and feveral Species, which he fuppofes proceed from a Mixture of the Spirit of Vitriol, Salt and Alum; which Minerals are found partly fimple and partly mixed, more or lefs with others in the Cavities of the Earth, especially with Iron. He proves this the true Cause of Acidulæ. 1. Because almoft wherever thefe acid Fountains break out, there are found Mines of Vitriol, Salt and Alum.